a) Field of the Invention
This invention relates to a film-made sheath making use of a shrinkable film.
b) Description of the Related Art
In the dental care field, cameras which are useful ful for taking pictures inside oral cavities (hereinafter called "intraoral cameras") have been finding utility recently. FIG. 4 is a perspective view of an intraoral camera 1. The intraoral camera 1 is provided with a rod-shaped, mouth insert portion 3, a handle 5 and a cord 7. The mouth insert portion 3 is provided at a free end portion thereof with light portions 3a for illuminating an object to be imaged and also with a light-receiving portion 3b for receiving light from the object. The free end portion of the mouth insert portion 3 is inserted into the oral cavity of a patient. A particular part of the oral cavity, an image of which is desired, is illuminated by the light portions 3a, and light reflected from the particular part is received through the light-receiving portion 3b. The light so received is converted into video signals by CCD sensors or the like, and the video signals are transmitted to an external control box via the cord 7. At the control box, an image of the particular part is displayed on a monitor or the like for use in checking and/or treatment.
From the viewpoint of dental hygiene (specifically, the prevention of infectious diseases or the like), a film-made sheath formed of a transparent resin or the like is applied over the mouth insert portion 3. A new film-made sheath is applied whenever the intraoral camera is used for a different patient. For a conventional example, reference may be had to U.S. Pat. No. 4,757,381. Whenever such a conventional film-made sheath is used, it is, however, necessary to stretch the film-made sheath in a certain specific direction to avoid formation of wrinkles at a part of the film-made sheath, said part being brought into contact with the light-receiving portion 3b, because no good image would otherwise be available.
With the method that features the stretching of a film-made sheath in a certain specific direction as described above, wrinkles cannot be eliminated fully. To fully avoid formation of wrinkles, the film-made sheath has to be stretched in plural directions. This however requires both labor and time for applying the film-made sheath.